Beam therapy unit



Aug. 18, 1953 D. 1'. GREEN 2,649,549

BEAM THERAPY UNIT Filed Feb. 8, 1951 /A/ VE N 70/? 00/VALO THOMAS Giff/(l ill slope is also conditioned by the angle through which the container is to be tilted. Outlet I4 is located as shown in Figure 2 with its apex adjacent to source of radiation I8 and extends to the base of container I I. A window I5 which may be of stainless steel or of other material having a low absorption is horizontally disposed near the apex of outlet I4 to provide a seal between the interior of outlet I4 and source of radiation I8. the lower part of outlet I4 is another window It which may also be of stainless steel and which should be slightly sloped to facilitate draining of the mercury and to increase the angle through which the container can be revolved. The distance between window I 6 and source I 8 should be sufficient, having regard to the comparative densities of the mercury in outlet I4 and the material of which container I I is composed, to afi'ord pro tection against radiation approximately equal to the protection given in other directions. As a safety measure, an additional window I! flush with the exterior of container I I. may be located below window IS.

The angle through which the unit illustrated in Figure 2 can be revolved about an axis perpendicular to the paper upon which this figure is drawn will be dependent upon two limiting positions. The unit in Figure 2 cannot be rotated counterclockwise past the position at which window I6 is horizontal without trapping mercury which will not be driven out of outlet port I4 by the compressed air. Similarly the unit cannot be rotated in a clockwise direction past the position at which side I8 of outlet port I4 is horizontal. The angle through which the unit can be revolved without interference with its operation henceforth designated as "the angle of tilt will not therefore be greater than one hundred and eighty degrees (180) minus the dihedral angle between the surface of window I6 and a plane tangential to side I8 of cone shaped outlet I4 at the lowest point of intersection of side I8 and window I6. Another way of expressing this is:

0:180-(a-B) where 0 is the angle of tilt a is the base angle of the cone 18 is the maximum angle of slope of window I6.

Where window I 6 is irregular in shape the effective angle of slope for draining purposes will be its maximum angle; which indicates that a slight increase in the angle of tilt may be obtained by providing an annular drain around the circumference of window I6 the trough of which is at a greater slope than the remainder of the window or alternatively draining pipes could be provided in window I6. The object of many of the limitations to the angles of slope from the horizontal of the integers to be described is to preserve the angle of tilt from being limited by factors other than the slopes of side I8 and window I6.

Two pipes, I9 and 28 connect outlet I4 to a reservoir 2I. The angle of slope of pipes I9 and 28 should be less than that of side I8 and greater than that of sloping window I6, in order that the mercury may be driven upward into reservoir 2! through pipes I9 and 28 at all effective angles of tilt. In order that the angle of slope of pipes I9 and 28 be less than that of side IE, it is necessary that the pipes branch out on either side of outlet I4 as illustrated in Figure 1. A

4 horizontal pipe 22 joins pipes I9 and 28 to the bottom of outlet I4. A sump 23 provides access between pipe 22 and the interior of outlet I4 and should be so shaped that there will always be a mercury seal to prevent air from escaping from the interior of outlet I4 through pipe I9 or 28 into reservoir 2I. Reservoir 2I should be.

shaped so that its base 24 is at an equal or greater slope than window I6 and its interior side wall 25 is at an equal or lesser slope than side I8 in order that there will always be a downward inclination to the base and interior side walls of the reservoir throughout the efiective angle of tilt of the unit. If the exterior of container II is cylindrical in shape as illustrated in Figures 1 and 2, reservoir 2I will be crescent shaped and either horn ofthe crescent should be connected to pipes I9 and 28 as at 26 and 21. The volume of reservoir 2I should be such that when the mercury has been fully driven out of outlet I4 into sump 23, a space is left in reservoir 21 containing compressed air which exerts a pressure not greater than the pressure used to drive the mercury up into reservoir 2I On the same side of outlet I4 as reservoir 2!, is an inlet pipe 28 for the admission of compressed gas, preferably air. A low density fluid may alternatively be used if necessary modifications to the system are made. Pipe 28 branches into a pipe 29 which runs to the apex of outlet I4 and pipe 38 which runs to the base of outlet I4 at a point which is diametrically opposite to the centre of sump 23. In order to prevent mercury from flowing out through pipe 29 or 38 at various angles of tilt, the slope of pipe 29 should be greater than that of window It and the slope of pipe 38 should be equal to or less than the slope of side 2I. Branch pipes 29 and 38 are provided so that whatever the angle of tilt, com

pressed air can be supplied to the upper level of the mercury in outlet I4 rather than being bubbled through the mercury.

Sufiicient mercury or other high density fluid having a high absorbtivity to radiation is provided completely to fill outlet !4 and partially to fill pipes I9, 28, 29 and 38. When compressed air is supplied through pipe 28, the mercury is forced through pipes I9 and 28 up into reservoir 2I and outlet I4 is filled with compressed air. The result is to release the beam since the high density material which filled outlet I4 has now been replaced by low density material. When pipe 28 is opened to the atmosphere, the air in outlet I4 will be released to the atmosphere and the mercury in reservoir 2! will flow into outlet I4 filling it under the influence of gravity and the pressure of the air which has been compressed in reservoir 2|. 7

When the mercury is in outlet port I4 the air in reservoir 2| is preferably at atmospheric pressure so that it will be compressed as mercury is forced into the reservoir to form an air cushion against the mercury flowing into the reservoir when the beam is released and to assist in overcoming the initial inertia of the mercury when the mercury is returned to outlet port I 4 to close ofi the beam. The resistance to flow caused by the capillary action of passages 28, 29 and 38 provides a cushioning action against the surge of the mercury when the beam is closed oil.

The operating controls are schematically illustrated in Figure'B in which an air compressor 3I supplies air through an air hose 32 to pipe 28. A pressure switch 33 with a low differential, which is connected by a communicating passage access 3.4 to reservoir 2| switches-off the air compressor 3| when all of the mercury has lbeeniorced out of the interior oi. outlet :port tlil'andait alsorprovi-des a convenient means of adjustment of the volume of mercury forced out ofoutlet |4since the pressure produced in reservoir 2| is ,a direct function of the reduction of the "volume :of air in reservoir '2.| which .in turn is equal to the volume ofmercury forced out of outlet "port M. A solenoid valve .35 is provided to release airf-rom outlet port l-4 through "pipe 28 into the atmosphere. Asource of electrical energy 3.6:operates aircompressor 3| and closes solenoid valve .35

until the circuit .is broken by "opening .switch :3;'| orby pressureswitchi33. Switch .31 islocated 550 that it will turn off :theair. compressor and open solenoid valve 35, whereas :switch 1.33 is positioned so "that it will switch :ofi airzcompressor 3.1 but will not .open solenoid "valve .35.

The beam is turned on by closing switch -;3;F| which may be remotely located. This :starts .the

air compressor 3| and at .the same time closes the mormally open solenoid operated -:valve .515. The air compressor 3% then builds up air-pressure .:in outlet :port 24 until the volume oi-mercury displaced compresses the air in reservoir 2] to the point "at which the pressure switch '33 (normally closed) opens and {thus stops the .compressor 3|. If there .is leakage anyW-hereiin the system above the mercury levelin outlet 14, when the level of mercury in .outlet M has as a consequence risen to a :point which causes aichan'geiin the pressure in reservoir 2| equal :to the difierential of switch .33, the "compressorstarts again and roe-establishes .the mercury level "in outlet port I4- As long as switch .31 is closed the mercury level in outlet port :-|-4 is :maintained between these .two lim'itsand by choosingthe difl ferential of the switch 3.3., the ratio of the volume of reservoir 2! to the volume of outlet port i l, the air pressure in .outlet 14 above the memcury, and thegshapeanddimensions f sump 23, the differential of the mercury level in outlet port it .in the on condition can .be made very small and maintained between two knownpoints belowthe level of'window It. To turn the unit oh the switch .331 is opened which will open the solenoid valve 35 and release the air pressure in outlet port l4 until it becomes equal to thatof the atmosphere. The mercury in 'reservoir 2! will then flow into outlet l4, due to the force exerted by gravity and assisted by the air pressure in reservoir 2|. If the source of electrical current or any part of the chain of equipment preceding the mercury level in outlet i4 fails the unit will turn ofi. It cannot become stuck in the on position short of failure to open of solenoid valve 35. A simple manually operated valve may be added in parallel with valve 35 which could be operated with a lon rod at a safe distance to safeguard against this eventuality.

It will be appreciated from the foregoing that a simple practical unit which operates positively to close off the beam has been designated based on the principle of replacing material of high absorbtivity such as mercury by material of low absorbtivity such as compressed air.

I claim:

1. In a beam therapy unit including radioactive material providing a source of high energy gamma radiation within a container capable of absorbing radiation in excess of a safe quantity, apparatus for releasing and controlling a beam comprising a conical shaped outlet port, a reservoir .at a higher level than said outlet port, connecting passages between the base or the outlet "port and the base 'of the reservoir, .sufficient :mercury within .said outlet ::port :to absorb radiation in excess of a safe amount, a window sealing saidfoutlet port to preventimercuryfrom escaping through the open end of said outlet port while being capable of allowing the transmission -..of :quantities I of radiation of therapeutic value, and "means for :forcing compressed gas into said .outlet portto drive the mercury from the outlet port into the reservoir :releasing 'a beam :of radiation, means-comprising said compressed gas :for maintaining said liquidrnaterial exteriorly of said outlet port and means for IE- leasing the compressed gas to .allow the mercury to returnto said outlet port to close off said beam.

2. In :a beam therapy unit rotatable about a horizontal axis and including radio-activetmaterial providing a source of high energy gamma radiation within a container which absorbs radiatien'in excess of a safe quantity, apparatus for :releasing and controlling the beam comprising aconical shaped outlet port, a sloped :window sealing said :outlet port to prevent mercury from escaping through the open end thereof while being capable of allowing the transmission of quantities of radiation of therapeutic value, a reservoir at a higher lever than and laterally displaced "from said outlet port having a base at an equal or greater'slope than that of :said window and having .an .inside wall of an equal or lesser slope than the base angle of said conical shaped outlet port, .a sump at the lower end of said window, passages linking the base of the sump with the base of the reservoir, suflicient mercury within said outlet port to prevent the transmission of radiation in excess of a safe amount and meansfor supplying compressed gas tosaid outlet port to displace the mercury, forcing it .into said sump passages and reservoir, and means for allowing the mercury to return to said outlet port to close off said beam.

3. Anapparatus as in claim 2 wherein the means for-supplying compressed gas includes a branched passage connecting a source of compressed gas to apoint near the apex of the outlet port and to a point near the base of said outlet port at the upper end of the sloped window so that compressed gas will be supplied above the level of the mercury at any angle of tilt of the unit.

4. In a beam therapy unit which may be tilted about a horizontal axis including radioactive material providing a source of high energy gamma radiation within a container which absorbs radiation in excess of a safe quantity, apparatus for controlling the beam comprising a conical shaped outlet port, a sloped window sealing said outlet port to prevent mercury from escaping through the open end thereof while being capable of allowing the transmisison of quantities of radiation of therapeutic value, a reservoir at a higher level than and laterally displaced in the direction of the higher end of the sloped window from said outlet port, having a base at an equal or greater slope than that of said window and having an equal or lesser slope than the base angle of said conical shaped outlet port, a sump capable of providing a mercury seal at all angles of tilt of the beam therapy unit, passages diverging on either side of the outlet port linking the base of the sump with the base of the reservoir, suflicient mercury within said outlet port to prevent the transmission of radiation in excess of a safe amount and means for supplying compressed gas to said outlet port to displace the mercury forcing it into said sump passages and reservoir; said last mentioned means comprising a passage forking into an upper branch at a greater slope than said window connecting a source of compressed gas to a point adjacent to the apex of said outlet port and a lower branch at a lesser angle of slope than the base angle of the outlet port connecting the source of compressed gas to a point near the base of said outlet port and at the upper end of the sloped window so that compressed gas will be supplied'above the level of the mercury at any angle of tilt of the unit, and means for releasing the compressed gas from said outlet port to allow the mercury to return to said outlet port to close off said beam, and means for controlling the amount of mercury displaced and forced into the reservoir.

5. An article as in claim 4 in which the means for controlling the amount of mercury displaced and forced into the reservoir comprises pressure responsive means operably connected to the means for supplying compressed gas.

6. An article as in claim 4 in which means are provided to rotate the therapy unit through an angle of tilt defined by the position in which the window is horizontal and the position in which the side of the outlet port opposite the base of the window is horizontal.

'7. An article as in claim 4 wherein the means for supplying compressed gas comprises an electrically operated air compressor connected by an air hose to said branched passages, and wherein the means for controlling the amount of mercury displaced comprises a pressure sensitive switch connected in series with the air compressor and responsive to changes in pressure within the reservoir, and wherein the means for releasing the gas from the outlet port comprises a solenoid valve connected in parallel with the air compressor and the pressure sensitive switch, and wherein a switch is inserted in series with both the air compressor and solenoid circuits.

8. In a beam therapy unit including a continuing source of radiation and a container having a low transmissibility to radiation enclosing said source and having an outlet port for the emission of a beam, apparatus for controlling the beam comprising gravity operated means for supplying a liquid material of low transmissibility to radiation to close off said outlet port, means for removing said liquid material from the outlet port to open said outlet port comprising displacement of said liquid material from the outlet port to a higher level than said outlet port by compressed gas, means comprising said compressed gas for maintaining said liquid material eXteriorly of said outlet port, means for releasing the compressed gas from the outlet port to allow the liquid material to pass into the outlet port to close off the beam and means having a high transmissibility to radiation to prevent said liquid material from escaping through the open end of said outlet port.

9. In a beam therapy unit including a continuing source or radiation within a container capable of absorbing radiation in excess of a safe quantity, apparatus for releasing and controlling a beam comprising an outlet port, a reservoir at a higher level than said outlet port sufficient high density liquid material within said outlet port to absorb radiation in excess of a safe amount, connecting means for transferring the liquid material between the base of said outlet port'and the base of said reservoir, a window sealing said outlet port to prevent the liquid material from escaping through the open end of said outlet port while being capable of allowing the transmission of quantities of radiation of therapeutic value, means for forcing compressed gas into said outlet port to drive the liquid material from the outlet port into the reservoir releasing a beam of radiation and means for allowing the liquid material to return to said outlet port to close off said beams.

DONALD THOMAS GREEN.

References Cited in the file of this patent UNITED STATES PATENTS Number Name Date 2,373,214 Wolkenhauer Apr. 10, 1945 2,537,011 Aparicio Jan. 9, 1951 FOREIGN PATENTS Number Country Date 438,147 Great Britain Nov. 12, 1935 

